Connections of Josses Hill said they are going to supplement the Peterborough Chase winner at the confirmation stage, while the Thistlecrack team are still giving the Christmas feature serious consideration.
Coneygree was ruled out after failing to sparkle in a gallop on Saturday.
Connections of the Mark Bradstock-trained gelding were not happy with his work and feel the 2015 Cheltenham Gold Cup hero is below par.
“He didn’t work well on Saturday and he’s just not right,” said Bradstock’s wife and assistant, Sara.
“I just know he’s not himself. We’re not taking any risks. He is fragile and we want him to be completely on song when he runs.
“We’ll obviously take veterinary advice and then I’m sure the horse will tell us when he’s right again.
“I know every breath he takes, I know every step he takes, I know exactly how he is and he’s just not feeling good.
“We’ll still hopefully on for the Gold Cup, and maybe something before that.”
Coneygree returned from a year off the track last month when second to Cue Card in the Betfair Chase at Haydock and a rematch between the two over Christmas had been greatly anticipated.
Bookmakers’ reaction was to cut last year’s winner Cue Card to a general 4-5 favourite, while his Colin Tizzard-trained stablemate Thistlecrack was given a quote of 11-8 with a run.
His participation has yet to be confirmed as last season’s champion staying hurdler is also in contention for the 32Red Kauto Star Novices’ Chase on the same card.
When asked if Coneygree’s defection will influence down which route Thistlecrack will head on Boxing Day, John Snook, who owns the horse with his wife, Heather, said: “It makes no difference whatsoever.
“I’ve heard about Coneygree, which is a shame for them.
“We do know, though, that the Bradstocks will do the best for their horse and think the world of him – just like we do with Thistlecrack.
“I’ll speak to Colin at some point, but the one thing about racing is that if you plan too far ahead, it can kick you in the teeth.
“The most important thing is to make sure the horse is sound and well and we get to Kempton on Boxing Day, one way or another.
“I’m looking forward to whichever way we go. I’m very lucky to have such a nice horse.”
Josses Hill would be tackling three miles for the first time after owner Alan Spence said he would be added to the field at a cost of £10,000.
The Nicky Henderson-trained eight-year-old is unbeaten this season, with a comeback success over an extended two and a half miles at Kempton in November followed up by an accomplished victory in the Grade Two Peterborough Chase at Huntingdon.
Confirming the news, Henderson tweeted: “Josses Hill will be supplemented for the King George. He likes @kemptonparkrace & deserves to take his chance.”
Unowhatimeanharry cemented his status as Britain’s leading staying hurdler with another superb display to land the JLT Long Walk Hurdle at Ascot on Saturday.
The eight-year-old was one of the success stories of the last campaign, completing a five-timer in the Albert Bartlett Novices’ Hurdle at the Cheltenham Festival, but even trainer Harry Fry conceded he would need to raise his game significantly if he was to make a real splash this term.
He did just that on his return to action in last month’s Long Distance Hurdle at Newbury and was the 6-5 favourite to extend his winning sequence to seven on his return to Grade One level.
Barry Geraghty’s mount won the Long Walk in authoritative style, emerging from the Berkshire gloom to score by four and a half lengths from Lil Rockerfeller.
Fry said: “We’re relying on the jockey’s report (because of the fog), but Barry said it was a proper Grade One test and he’s had to work hard.
“We’ll have a chat to Barry and the team and see where we go, but the races are sort of there – the Cleeve Hurdle (at Cheltenham) and hopefully the big day (World Hurdle) in March.
“The dream goes on.”
Brain Power ran out an accomplished winner of the Wessex Youth Trust Handicap Hurdle on a big day for Nicky Henderson.
The 12-1 chance came home five lengths clear, with stable companion Consul De Thaix getting up to beat Fergall to the runner-up spot.
Stablemate Top Notch earlier secured a third successive victory over fences in the GL Events Owen Brown Graduation Chase.
Henderson said: “We will keep him at two-five or two and a half miles at a good gallop.”
The Seven Barrows handler was also significantly on the mark at Haydock as top-class novice hurdler Buveur D’Air made an impressive start to his chasing career. Henderson added: “We could look at Ireland – go and chase Min, or something like that – how about that for fun?”
Yorkhill made a flying start to life over fences with a bloodless victory at Fairyhouse and was promptly cut in the betting for the JLT Novices’ Chase at the Cheltenham Festival.
Trainer Willie Mullins said: “He could stay at two miles or go up in trip just depending where his next run fits in.”
Death Duty took his unbeaten record over smaller obstacles to three with an emphatic performance in the Navan Novice Hurdle at the County Meath track on Sunday.
The five-year-old was one of four winners on the card for Gordon Elliott, who said: “He will go now for the Grade One (Lawlors Hotel) novice hurdle at Naas (January 8).
“He looks an Albert Bartlett type.”
Elliott was also on the scoresheet in the feature race at Thurles as Shattered Love took advantage of the fall of odds-on shot Asthuria to take Listed honours in the Horse & Jockey Hotel EBF Boreen Belle Mares Novice Hurdle at Thurles.